1. Field of Invention
This invention pertains to an electronic sensor used for triggering a passenger or occupant restraint system such as an airbag in a motor vehicle, and more particularly to a sensor which detects events requiring such restraint by using an electronic accelerometer.
2. Description of the Prior Art
In the following, the term passenger shall be used to refer to any occupant in a motor vehicle, including the driver. Breed Automotive Technologies, Inc. (BAT), the assignee of the present invention has been very successful in developing various crash sensors for motor vehicle passenger restraint systems. These sensors include ball-in-tube electromechanical sensors, such as the one illustrated in U.S. Pat. No. 4,329,549, which consists of an elongated tubular chamber holding a ball made of a ferromagnetic material. At one end of the chamber, the sensor is provided with a magnet for biasing the ball at a preselected force. At the other end, the chamber is provided with two electrical contacts. The sensor is mounted in the vehicle with the ball being positioned against the back of the chamber when no deceleration occurs by the biasing force of the magnet. The sensor is positioned in such a manner that when the vehicle experiences a deceleration in excess of the biasing force of the magnet, the ball moves through the tubular chamber until it hits the electrical contact blades. The ball is made of or coated with an electrically conductive material so that when it reaches the contacts, it establishes an electrical path therebetween. In other words, the ball and contacts cooperate to form an electrical switch which closes when the vehicle is involved in a serious crash. The movement of the ball is damped by the air in the tubular chamber. Mechanical sensors are also known wherein, as described in U.S. Pat. No. 4,573,706, gas damped balls are used to trigger igniter caps.
Motor vehicles are now provided or will be provided with various electronic devices including antilock braking systems, electronically adjusting suspension systems, passenger position indication systems and so on. All these systems provide information which may be useful for the operation of passenger restraint systems. However, this information cannot be easily integrated with systems using electromechanical sensors.
Crash sensors using electronic accelerometers such as piezo-resistive, piezo-capacitive, piezo-voltaic and piezo-electric devices and others have been suggested previously, however they have not provided satisfactory performance especially in crashes which involve a small portion of a vehicle's frontal cross section such as crashes into poles, trees, etc.